Monik Jindal, owner of Pal Khaad Store in New Grain Market, was in his shop when the man entered inside and shot him from point-blank range last night, they said.
The motive of the crime remains unknown, the police said.
His mother, Padma Rani, after hearing the news of the killing, died of shock, they said.
The labourers working nearby said they saw a man running towards the main gate of the market after they heard a gunshot, the police said.
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There was a CCTV in victim's shop too. The police sent the footage to the IT cell as it was password protected, they said.
Punjab police Inspector General AS Rai visited the crime spot and assured that criminals would be nabbed soon.
Jindal's body has been sent to Nabha civil hospital for postmortem.
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